1. Field of the Invention
This invention relates to an optical apparatus having a lens driving device.
2. Related Background Art
Auto focus mechanisms in photo-taking lenses for video cameras have heretofore included an auto focus device which emits infrared light and meters light impinging on and reflected by an object, and an auto focus mechanism which meters the contrast of light passed through a photo-taking optical system by a CCD (solid state image pickup element) and judges in-focus by the value of the contrast having reached a peak. Any of these is such that a focusing lens is driven by an actuator in accordance with instructions from a distance measuring device to thereby perform the focusing operation.
Particularly in the latter auto focus device of the contrast detection type, the combination thereof with an inner focus optical system which pursues the compactness of the optical system has often been seen in recent years. As an example of the prior art, as shown in FIG. 5 of the accompanying drawings, a focusing lens holding frame 200 is designed to be parallel-movable in the direction of the optical axis by two guide shafts 300 and 400. A rack 500 meshing with a lead screw 800 formed on the shaft of a stepping motor 900 is mounted on a portion of the lens holding frame 200.
However, according to such structure, if the two guide shafts 300 and 400 for moving the lens are not parallel to the lead screw 800 which is the shaft of the stepping motor 900, an angular movement is created in the rack 500, whereby the movement of the lens holding frame 200 becomes unsmooth. Therefore, in order to ensure the degree of parallelism of these members, it has been practised to increase the accuracy of the parts or provide a mechanism for adjustment. As a result, a long time has been required for assembly, or a highly accurate and expensive part molding machine has been necessary to increase the accuracy of the parts.
So, in order to solve such problems, there has been devised a device as disclosed in Japanese Laid-Open Utility Model Application No. 2-71155 (its corresponding U.S. Patent has not yet been ascertained).
This device is such that a rack and a lens holding frame are connected together by a flexible connecting member, and the connecting member comprises, for example, a relatively thin spring member, and is intended to have rigidity for the movement of the lens in the direction of the optical axis and to have flexibility in a direction perpendicular to the optical axis.
In this device, however, to provide sufficient flexibility, it is necessary to make the connecting member thin, and to provide sufficient rigidity in the direction of the optical axis, it is necessary to make the length of the connecting member sufficiently great in the direction of the optical axis. This has led to the problem that an optical accessory such as a lens barrel using the device disclosed in Japanese Laid-Open Utility Model Application No. 2-71155 becomes bulky.